Improved ionic solid/viologen hybrid electrochromic device using pre-bleached Prussian-blue electrode

The authors demonstrate how a simple step of loading an electrochromically active Prussian blue (PB; an ionic solid) electrode with Li⁺ ions can help in achieving a more efficient viologen based solid state hybrid electrochromic device. To accomplish this, two different devices, with and without Li⁺ ion loaded PB electrodes, have been fabricated. These devices have been compared in terms of their current-voltage response, bias dependent optical modulation and corresponding colour switching to establish the role of Li⁺ ion in charge transport and charge balancing involved during bias induced redox mediated colour switching of the two devices. The Li⁺ containing PB electrode device exhibits a superior performance with twice (40%) the value of colour contrast (20%), quick response switching (1.3 s), excellent stability (8400 s) and better power efficiency as compared to the device containing as-synthesised PB electrode. A mechanism has been proposed to explain the role of the Li⁺ ion which is later substantiated using bias-dependent in situ Raman spectroscopic evidences.